Nitrous Oxide Emissions from In Situ Deposition of ¹⁵ N-Labeled Ryegrass Litter in a Pasture Soil

Abstract

During pasture grazing, freshly harvested herbage (litterfall) is dropped onto soils from the mouths of dairy cattle, potentially inducing nitrous oxide (N 2 O) emissions. Although the Intergovernmental Panel on Climate Change (IPCC) recommends accounting for N 2 O emissions from arable crop residues in national inventories, emissions from the litterfall of grazed pasture systems are not recognized. Th e objective of this study was to investigate the potential of litterfall to contribute to N 2 O emissions in a fi eld study located on a pasture site in Canterbury, New Zealand (43°38.50′ S, 172°27.17′ E). We applied O likely resulted from ammonifi cation followed by a coupling of nitrifi cation and denitrifi cation during litter decomposition on the soil surface. Th e emission factor of the litter deposited in situ was 1.2 ± 0.2%, which is not substantially greater than the IPCC default emission factor value of 1% for crop residues. Further in situ studies using diff erent pasture species and litterfall rates are required to understand the microbial processes responsible for litter-induced N 2 O emissions.

Ecological controls on N<sub>2</sub>O emission in surface litter and near-surface soil of a managed grassland: modelling and measurements

“…3, 4). This model finding is consistent with the experimental finding of Pal et al (2013) (Figs. 3g, 4g).…”

“…bulk density, water retention). The N 2 O driving these emissions in managed grasslands is thought to be generated within the upper 2 cm of the soil profile (van der Weerden et al, 2013) and in surface litter left by grazing or harvesting (Pal et al, 2013) so that diurnal heating and precipitation events that cause rapid warming and wetting of the litter and soil surface may cause large but brief emission events. These events are thought to be driven by increased demand for electron acceptors by nitrification and denitrification, a reduced supply of O 2 by which these demands are preferentially met, and therefore increased demand for alternative acceptors NO The magnitude of N 2 O emission events in managed grasslands generally increases with the amount of N added as urine, manure or fertilizer and with the intensity of defoliation by grazing or cutting (Ruzjerez et al, 1994).…”

Annual burning of a tallgrass prairie inhibits C and N cycling in soil, increasing recalcitrant pyrogenic organic matter storage while reducing N availability

“…This indicates a progression in the decomposition of litter, with DOM and microbial products contributing to the accumulation of litter decomposition products in the clay fraction over time (Grandy & Neff, ; Cotrufo et al ., ). The decrease in the amount of litter‐derived N in the LF and sand‐sized fraction over time provides evidence of active microbial utilization and mineralization of litter N as it is decomposed over time at the IB site (Pal et al ., ). The over 96% contribution of the py‐OM to the LF highlights the need to reconsider the mean residence time of the LF in frequently burned ecosystems (Trumbore, ).…”

Using stable isotopes to follow excreta N dynamics and N2O emissions in animal production systems

“…Ruminant grazing of pasture and forage crops causes fresh litterfall, as animals fail to ingest all harvested herbage (Lodge et al, 2006;Campanella and Bisigato, 2010;Pal et al, 2012). One study, replicating a grazing-induced litterfall event, used 15 N tracer to show that fresh litter deposition contributed to the N 2 O flux (1% of N applied) from the soil surface and enriched the soil inorganic-N pool (Pal et al, 2013). Experiments have also been conducted using 15 N-enriched N 2 to study the fate of biologically fixed N 2 .…”